When does the average velocity become zero?

The average velocity becomes zero when the total displacement (change in position) of an object over a certain time interval is zero. In other words, if an object moves back and forth, covering equal distances in opposite directions, its average velocity will be zero.

Mathematically, the average velocity (v_avg) is defined as the total displacement (Δx) of an object divided by the total time (Δt) taken to cover that displacement:

v_avg = Δx / Δt

If the object returns to its starting position after a certain time, then Δx will be zero, and consequently, the average velocity will also be zero.

Keep in mind that the average velocity being zero doesn't mean that the object was stationary during that time interval. It could have moved at varying speeds in different directions, but when you consider the overall change in position, it averages out to zero.